Theophrastus. Enquiry into Plants and Minor Works, translated into English by Arthur Hort (London, 1916), in 1025 bookmarked and searchable pdf pages. The download contains Loeb Classical Library volumes L70 and L79 in one file, and includes minor works On Odours and Weather Signs. Attached to the document is a multilingual HTML version of Enquiry into Plants. Wikipedia has an entry on Theophrastus (about 371 to about 287 B.C.), considered the "Father of Botany" in the West; and also an entry on this work Enquiry into Plants or Historia Plantarum. Books digitized by Google and compiled by Robert Bedrosian. See also volumes 3, 4, and 5 of the Natural History, by Pliny the Elder (23-79 A.D.), which deal with plants and also with remedies made from them: Volumes Guide to Pliny's Natural History.

Note: the Greek and English texts are best displayed with the pages "side by side" ("two up" or "facing"). Pdf readers (such as Foxit and Adobe) have this option under the menu item View/Page Display.

Theophrastus' Enquiry into Plants:

Book 1. The Parts of Plants and Their Composition
Book 2. Propagation, especially of Trees
Book 3. Wild Trees

Book 4. The Trees and Plants Special to Particular Districts and Positions
Book 5. The Timber of Various Trees and Its Uses
Book 6. Under-Shrubs

Book 7. Herbaceous Plants, Other than Coronary Plants: Pot-herbs and Similar Wild Herbs
Book 8. Herbaceous Plants: Cereals, Pulses, and 'Summer Crops'
Book 9. The Juices of Plants and the Medicinal Properties of Herbs